1. Field of the Invention
The present invention relates to a recording adjusting method and a recording power adjusting method as well as an optical information recording and reproducing device and an information recording medium for performing the recording adjusting method and the recording power adjusting method.
2. Description of the Related Art
Currently, a compact disc (CD), a digital versatile disc (DVD), a blu-ray disc (BD), and the like have been widely used as optical discs which are optical information recording media. In recent years, a BDXL has also been commercialized, which is an advanced BD having an increased number of data layers, i.e., three or four data layers. There are various types of optical discs, such as read only memory (ROM), recordable (R), and rewritable (RE) discs.
Information is recorded in or reproduced from the optical disc by using laser light. In recording information in the recordable or rewritable optical disc, laser light is emitted onto a data layer to change the optical characteristics of the data layer. At this time, the data layer experiences formation of a mark which is a region having changed optical characteristics and a space which is a region having unchanged optical characteristics. Information is recorded therein by combining marks and spaces. In contrast, in reproducing information, laser light having less power than in recording is emitted onto the data layer, and an amount of reflection light therefrom is detected. The reflection light amount varies depending on whether the laser light spot is on the mark or the space. Thus, the variation of the reflection light amount is used to reproduce the information.
During the aforementioned recording and reproduction performed on the optical disc, the position of a light spot is controlled by focus servo and tracking servo. The focus servo is a control of moving the focus of laser light in a vertical direction of the optical disc to always keep the focus on the data layer of the optical disc. The tracking servo is a control of moving the light spot in a horizontal direction (an in-plane direction) of the optical disc to cause the light spot to always follow a row including the marks and the spaces (hereinafter, referred to as a track). These controls enable the light spot to scan the track of the data layer at all the time during the recording and reproduction.
The light spot position control by the tracking servo is performed based on a tracking error signal (TES) correlated with an amount of offset from a track. The TES is a signal calculated from a diffraction pattern of reflection light from the track. Typical examples of a TES generation method are a differential phase detection (DPD) method and a push-pull (PP) method. The DPD method uses diffractions caused by marks and spaces included in the track, and thus is mainly used for a ROM optical disc having marks formed in the form of recessed pits. The PP method is mainly used for recordable and rewritable optical discs. The PP method uses diffractions caused by a groove which is a guide groove in each of tracks provided in data layers of the discs.
By using FIG. 1, a description is given of a principle of generation of a TES based on the PP method utilizing diffraction light caused by a groove (hereinafter, referred to as a PP-TES). FIG. 1A is a schematic diagram of a PP-TES generation circuit including: a photo detector 101a divided into two regions in parallel with a groove; and a subtractor 102a. The photo detector 101a receives reflection light in regions A and B, and the light intensities thereof are varied by the diffraction caused by the groove, according to an amount of offset of the light spot from the groove. Hence, the subtractor 102a calculates a difference between signals from A and B of the photo detector 101a, so that a PP-TES is generated. FIG. 1B-1 is a schematic diagram showing a case where a spot 101b moves while crossing grooves 102b, and FIG. 1C is a schematic diagram of a PP-TES generated at this time. As seen from FIG. 1C, when the light spot is on the center of each of the grooves, the PP-TES is at the zero-crossing of a falling edge (or a zero crossing of a rising edge, depending on the groove phase). Thus, the light spot 101b is kept on the track under such control that the PP-TES can always coincide with the zero crossing. Such tracking servo can be performed by using a PP-TES generated also from pits 104b of a ROM optical disc as shown in FIG. 1B-2. In this case, a light spot 103b passing a pit causes the PP-TES to have a certain amplitude, whereas the light spot 103b passing between pits causes the PP-TES to have an almost zero amplitude. However, the spot moving rate is higher in a parallel direction of the tracks than in a vertical direction thereof, which is high enough to obtain an average PP-TES similar to that in FIG. 1C.
The DPD method is a method of generating a TES from pits of a ROM optical disc more stably than the PP method. A method of generating a TES used in the DPD method (hereinafter, referred to as a DPD-TES) will be described by using FIG. 2. FIG. 2A is a schematic diagram of a DPD-TES generation circuit. The DPD method uses a photo detector 201a divided into four regions. Thus, the reflection light received by the photo detector 201a is divided into four components A, B, C, and D. The light intensity ratio between a sum of the diagonal components A+C and a sum of the diagonal components B+D varies depending on the diffraction caused by a pit edge. Hence, on the assumption that a light spot 201b passes a row including pits 202b as in FIG. 2B, a description is given below of a DPD-TES generated at this time.
Firstly, adders 202a generate an (A+C) input signal S211 and a (B+D) input signal S212 from signals of light received by the detector 201a. FIG. 2C schematically shows the input signals. The relative position of the signals of light at pit edges varies depending on the offset directions of the light spot from the track. The signals S211 and S212 are processed to have a boost in high frequency components thereof by high-frequency boosters 203a and are respectively converted into an A+C binary signal S221 and a B+D binary signal S222 by binarizers 204a. FIG. 2D schematically shows the binary signals S221 and S222. By using the binary signals S221 and S222, a phase difference detector 205a detects a phase difference between the A+C binary signal S221 and the B+D binary signal S222. The phase difference detector 205a generates a leading phase pulse signal S231 in a case of a phase lead of the A+C binary signal S221, or generates a lagging phase pulse signal S232 in a case of a phase lag of the A+C binary signal S221. FIG. 2E schematically shows the signals S231 and S232 as well as signals S241 and S242 obtained by processing of LPFs 206a at the subsequent stage.
Lastly, a subtractor 207a calculates a difference between the signals S241 and S242, so that a DPD-TES is generated. FIG. 2F schematically shows the DPD-TES generated in the case shown in FIG. 2B as well as a differential signal S250 of the leading phase pulse signal S231 and the lagging phase pulse signal S232. The DPD-TES generated in the aforementioned manner is at the zero crossing of a falling edge when the light spot 201b is on the center of the track. Thus, the light spot 201b can be kept on the track under such control that the DPD-TES can always coincide with the zero crossing.
The tracking servo is controlled by the TES represented by those described above, and thus conventional optical discs have achieved highly accurate positioning in recording and reproducing information.
In efforts made to achieve a much larger volume optical disc in recent years, methods of increasing a capacity per disc by further increasing data layers from those of a BDXL have been reported in academic meetings and the like. A (grooveless) method of eliminating a groove structure from a data layer has also been proposed to simplify a production process for a medium with increased data layers. Non-patent document 1 reports a grooveless recordable optical disc having 16 data layers. A disc using this method has a servo surface of a groove structure in addition to the 16 data layers. Moreover, a recording and reproducing device includes an additional laser having a different wavelength for exclusive servo use, wherein the relative position of the laser and the spot used for recording and reproducing is fixed. Thereby, while performing tracking servo on the servo surface of the disc with the laser for exclusive servo use, the recording and reproducing device can perform recording or reproduction by using a recording or reproduction spot moving in synchronization with a servo spot, and thereby practically achieves the tracking servo on each data layer.